This project proposes the preparation and preliminary study of selenazolidine carboxylic acids as novel selenium delivery agents. Selenium is of growing importance in human health beyond its well-recognized role as a micronutrient. For example, selenium has exhibited exciting activity as a cancer chemopreventive agent against disease in several organs, caused by a variety of carcinogens. Selenium is also known for its toxicity, however, making the development of clinically valuable agents a distinct challenge that must be accomplished with extreme care and creativity. The selenazolidines represent "prodrug" forms of Lselenocysteine. They were designed to provide a continuous supply of the amino acid (as a source of selenium) at levels high and sustained enough to have therapeutic value but not high enough to produce toxicity. The current application will accomplish four specific aims: (1) Design, synthesize, and chemically characterize carefully selected prototypes of new subclasses of selenazolidine prodrugs to allow the development of critical structure-activity relationships; (2) Understand the chemical/biochemical breakdown of the selenazolidines; (3) Undertake animal studies in the well-established A/J mouse model to study toxicity of the novel agents, as well as their effect on basic biochemical parameters; (4) Expand animal studies to: (a) investigate the cancer chemopreventive activity of the new selenazolidines against a tobacco derived lung carcinogen; (b) explore varied administration schedules for cancer chemoprevention; (c) study selected selenazolidines in combination with vitamin E, vitamin C, or N-acetylcysteine (cysteine source) to enhance chemoprevention; and (d) study the preventive attributes of selected selenazolidines in selenium-deficient animals. These analogs are completely novel; it appears to be an entirely new approach in the selenium field and may allow the potential of selenium as a preventive and/or therapeutic agent in human disease to be clinically realized.